argin may be partially luminous, rendering the middle parts all the more obscure by the contrast.

A wonderful variety may also be produced by the shadow of one cloud falling upon another. The accompanying sketch furnishes an example of this. Sometimes the whole of a cloud projects a shadow through the air upon some other far distant cloud, and this again upon another, until at length it reaches the ground. The shadows of moving clouds may often be traced upon the ground, and they contribute greatly to modify the appearance of the landscape. A large number of small flickering clouds produce broken lights and shades which have an unpleasant jarring effect; but when the clouds are massive, or properly distributed, the shadows often produce a high degree of repose.

[Picture: Shadows of clouds]

Clouds are often seen to advantage in mountainous countries. Here the aspect of the heavens may be entirely different at different elevations. A single cloud in the valley may conceal the whole of the u